The immune system is a defense system found in its most advanced form in higher vertebrates. This defense mechanism provides rapid and highly specific responses which are used to protect an organism against invasion by pathogenic microorganisms. It is the myriad of pathogenic microorganisms which have principally caused the evolution of the immune system to its current form. In addition to protection against infectious agents, specific immune responses are thought to be involved in surveillance against tumor development, the pathogenesis of autoimmune diseases, and transplant tissue rejection.
T cells are the major regulatory cells of the immune system. The regulatory functions of T cells depend not only on expression of a unique T cell receptor, but also on expression of a variety of accessory molecules and effector functions associated with an individual T cell response (i.e., a cytotoxic response versus a response characterized by secretion of effector molecules such as lymphokines). It is this regulatory function that often goes awry in the development of autoimmune diseases, plays a large role in tissue graft rejection, and can be important in tumor rejection.
Specificity of T cell responses is conferred by a unique set of cell surface receptors expressed on individual lymphocytes, called clonotypic T cell receptors (TCR). Cognate ligands of the clonotypic TCR are antigen major histocompatibility complex molecules (MHC). T cell receptors recognize antigens in the form of small antigenic peptides presented by MHC molecules on the surface of antigen presenting cells. While the interaction between an antigenic peptide and an MHC is quite stable, generally displaying a high affinity (10xe2x88x929 M) and consequent long half-life of dissociation, the interaction between a T cell receptor and a peptide/MHC complexxe2x80x94the critical recognition event in triggering T cellsxe2x80x94is of relatively low affinity, between 10xe2x88x924-10xe2x88x926 M. As a result of this low affinity, the T cell response is driven by the interaction of many T cell receptors on the surface of an individual T cell interacting with multiple antigenic peptide/MHC complexes on the surface of the antigen presenting cell.
Antigen-specific T cells play major roles in normal physiologic immune responses and in many disease states. Hyperactivation of antigen-specific T cells targeted toward self antigens is the underlying basis for the majority of autoimmune diseases, including multiple sclerosis, arthritis, and diabetes. Conversely, inactivity of tumor antigen-specific T cells allows tumors to grow. Thus, activation of dormant or tolerant tumor-specific T cells has been a major goal of cancer immunotherapy. Other important medical phenomena, such as rejection of transplanted organs, depend on the activity of T cells specific for alloantigens expressed by these organs. Antigen-specific suppression of undesired T cell responses could potentially eliminate organ graft rejection.
The use of soluble monovalent reagents to monitor and modulate antigen-specific T cells is limited by the fact that T cell receptors interact with peptide/MHC complexes with relatively low affinities (28-30). Thus, soluble monovalent analogs of either T cell receptors or peptide/MHC complexes do not effectively regulate immune responses.
Soluble multivalent analogs of proteins involved in immune responses have been made. Such analogs include CD4/Ig chimeras (41, 42), CR2/Ig chimeras (43), and class I MHC/Ig chimeras (20). The influence of valence on ligand affinity of these analogs is variable. For example, CD4/Ig molecules do not have a higher affinity for their ligand than soluble monovalent CD4 molecules. Tetravalent peptide/MHC complexes have high affinity for specific T cell receptors. However, divalent MHC analogs do not have a high enough affinity to allow staining or regulating antigen-specific T cells. Thus, there is a need in the art for agents which can specifically induce or suppress T cells specific for antigens associated with infections, allergies, tumors, transplanted organs, and autoimmune diseases.
It is an object of the invention to provide a set of reagents which specifically and stably bind to and modulate antigen-specific T cells. This and other objects of the invention are provided by one or more of the following embodiments.
One embodiment of the invention provides a composition comprising a chimeric protein. The chimeric protein comprises an MHC molecule and an immunoglobulin chain. The chimeric protein associates to form molecular complexes comprising at least two chimeric proteins per complex. An antigenic peptide is bound to each MHC molecule. Each MHC molecule within the molecular complex is bound to an identical antigenic peptide.
Still another embodiment of the invention provides a vector encoding a chimeric protein. The chimeric protein comprises an immunoglobulin heavy chain and an MHC molecule. The immunoglobulin is not IgG-1. The immunoglobulin heavy chain is C-terminal to the MHC molecule.
Even another embodiment of the invention provides a composition comprising a chimeric protein which comprises an MHC molecule and an Ig chain. The chimeric protein associates to form molecular complexes comprising at least two chimeric proteins per complex. The immunoglobulin chain is not an IgG heavy chain.
Another embodiment of the invention provides a composition comprising a cell in which a chimeric protein is bound to the surface of the cell. The chimeric protein comprises an MHC molecule and an immunoglobulin chain. The chimeric protein associates to form molecular complexes comprising at least two chimeric proteins per complex. An antigenic peptide is bound to each MHC molecule. Each MHC molecule within the molecular complex is bound to an identical antigenic peptide.
Still another embodiment of the invention provides a method for treating a patient suffering from an allergy. A chimeric protein which comprises an MHC molecule and an immunoglobulin chain is administered to a patient at a dose sufficient to suppress a T cell response associated with an allergy of the patient. The chimeric protein associates to form molecular complexes comprising at least two chimeric proteins per complex. An antigenic peptide is bound to each MHC molecule. Each MHC molecule within the molecular complex is bound to an identical antigenic peptide. The antigenic peptide is an antigen to which the patient has an allergic response.
Even another embodiment of the invention provides a method for treating a patient who has received or will receive an organ transplant. A chimeric protein which comprises an MHC molecule and an immunoglobulin chain is administered to the patient at a dose sufficient to suppress an immune response to the transplanted organ. The chimeric protein associates to form molecular complexes comprising at least two chimeric proteins per complex. An antigenic peptide is bound to each MHC molecule. Each MHC molecule within the molecular complex is bound to an identical antigenic peptide. The antigenic peptide is an alloantigen.
Another embodiment of the invention provides a method for treating a patient suffering from an autoimmune disease. A chimeric protein which comprises an MHC molecule and an immunoglobulin chain is administered to the patient at a dose sufficient to suppress an immune response associated with the autoimmune disease. The chimeric protein associates to form molecular complexes comprising at least two chimeric proteins per complex. An antigenic peptide is bound to each MHC molecule. Each MHC molecule within the molecular complex is bound to an identical antigenic peptide. The antigenic peptide is one to which the patient expresses an autoimmune response.
Still another embodiment of the invention provides a method for treating a patient having a tumor. A chimeric protein which comprises an MHC molecule and an immunoglobulin chain is administered to the patient at a dose sufficient to induce or enhance an immune response to the tumor. The chimeric protein associates to form molecular complexes comprising at least two chimeric proteins per complex. An antigenic peptide is bound to each MHC molecule. Each MHC molecule within the molecular complex is bound to an identical antigenic peptide. The antigenic peptide is a tumor-associated peptide.
Another embodiment of the invention provides a method for treating a patient having an infection. A chimeric protein which comprises an MHC molecule and an immunoglobulin chain is administered to the patient at a dose sufficient to induce or enhance an immune response to the infection. The chimeric protein associates to form molecular complexes comprising at least two chimeric proteins per complex. An antigenic peptide is bound to each MHC molecule. Each MHC molecule within the molecular complex is bound to an identical antigenic peptide. The antigenic peptide is an infectious agent-associated peptide.
Even another embodiment of the invention provides a method of labeling antigen-specific T cells. A sample comprising antigen-specific T cells is contacted with a chimeric protein. The chimeric protein comprises an MHC molecule and an immunoglobulin chain. The chimeric protein associates to form molecular complexes comprising at least two chimeric proteins per complex. Each MHC molecule within the molecular complex is bound to an identical antigenic peptide. The antigenic peptide specifically binds to and labels the antigen-specific T cells.
These and other embodiments of the invention provide the art with tools and methods for modulating antigen-specific T cell immune responses.